Munin&mdash;the Raven Reports

Long-term monitoring with Munin is not restricted to system parameters. Why not monitor data of personal interest or data of interest to your colleagues?

How Individual Parameters Are Displayed

In addition to these variables related to the entire graph, you also can
specify details for each parameter the plugin monitors, so in the case
of the muc plugin, calling, boarding, departed, planned and
cancelled. The <parameter>.label variable sets the legend entry
for <parameter>.

<parameter>.draw specifies the type of diagram
the <parameter>
data is to be presented as. AREA asks the Munin master to draw the
relevant curve and fill the entire area between the x-axis and data point
with color. Parameter data of the drawing type STACK will be stacked
on top of this basic area. This way, we sum up all flights that, in the
current five-minute interval, are labeled calling, boarding and
departed. The airport timetable won't correct their departure time
later; they all count as dispatched at this point of time.

Flights tagged as planned and cancelled behave differently. For delayed
flights, the Munich Airport authorities will issue a new departure time
later. This way, the plugin will see planned flights twice:
as planned within their time slot according to schedule, and as
calling, boarding or departed at their actual time interval of
departure. That's why we draw delayed flights in a separate line of the
type LINE2. The number denotes the thickness of the line in pixels. A
LINE1 line is one pixel thick; a LINE2 line is two pixels, and a LINE3 line
is
three pixels. Cancelled flights won't reappear in the time schedule,
but as they will never depart, we also draw them as a separate line of
two pixels thick.

All this plugin output is written to the standard output. The
final version of our muc script is shown in Listing 1.

If we can do this by hand, the Munin master should generate some
nice little graphs and present them via the Web, as shown in Figure 3.

Figure 3. Munin creates daily, weekly, monthly and annual graphs. If
you want to preserve them for later comparison, you can write a cron job
that archives the relevant PNGs and/or RRD databases at certain points
of time.

Drawbacks

The simple way to write and integrate custom plugins is one of the
huge advantages of Munin—even the more complex wild-card plugins are no
big deal.

Unfortunately, simple sometimes also means simplistic. Although it is
possible to include Munin-generated diagrams in customized Web pages, Munin
does not provide any functionality to customize the Web pages generated
by the Munin master. Especially on sites with many hosts and plugins to
monitor, the simple approach that combines all daily and weekly graphs
in one page results in an extremely slow-loading overview page.

Another example of a rigid approach in the Munin architecture is
the fixed resolution of data. Not all data changes fast enough that the
five-minute interval is appropriate.

Unfortunately, a configuration option for individual plugins remains an
item on the wish list.
On the other hand, Munin allows quite powerful configuration for
plugins by means of environment variables set in the
/etc/munin/plugin-conf.d/ directory.

Because the documentation could be more extensive, and because the code isn't
well commented, the English and German users' mailing lists
remain helpful resources.

Geek Guides

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